# frozen_string_literal: true
# rubocop:disable Metrics/MethodLength
# rubocop:disable Metrics/ClassLength
# rubocop:disable Metrics/BlockLength
# rubocop:disable Style/Documentation

module Gitlab
  module BackgroundMigration
    class NormalizeLdapExternUidsRange
      class Identity < ActiveRecord::Base
        self.table_name = 'identities'
      end

      # Copied this class to make this migration resilient to future code changes.
      # And if the normalize behavior is changed in the future, it must be
      # accompanied by another migration.
      module Gitlab
        module Auth
          module LDAP
            class DN
              FormatError = Class.new(StandardError)
              MalformedError = Class.new(FormatError)
              UnsupportedError = Class.new(FormatError)

              def self.normalize_value(given_value)
                dummy_dn = "placeholder=#{given_value}"
                normalized_dn = new(*dummy_dn).to_normalized_s
                normalized_dn.sub(/\Aplaceholder=/, '')
              end

              ##
              # Initialize a DN, escaping as required. Pass in attributes in name/value
              # pairs. If there is a left over argument, it will be appended to the dn
              # without escaping (useful for a base string).
              #
              # Most uses of this class will be to escape a DN, rather than to parse it,
              # so storing the dn as an escaped String and parsing parts as required
              # with a state machine seems sensible.
              def initialize(*args)
                if args.length > 1
                  initialize_array(args)
                else
                  initialize_string(args[0])
                end
              end

              ##
              # Parse a DN into key value pairs using ASN from
              # http://tools.ietf.org/html/rfc2253 section 3.
              # rubocop:disable Metrics/AbcSize
              # rubocop:disable Metrics/CyclomaticComplexity
              # rubocop:disable Metrics/PerceivedComplexity
              def each_pair
                state = :key
                key = StringIO.new
                value = StringIO.new
                hex_buffer = ""

                @dn.each_char.with_index do |char, dn_index|
                  case state
                  when :key then
                    case char
                    when 'a'..'z', 'A'..'Z' then
                      state = :key_normal
                      key << char
                    when '0'..'9' then
                      state = :key_oid
                      key << char
                    when ' ' then state = :key
                    else raise(MalformedError, "Unrecognized first character of an RDN attribute type name \"#{char}\"")
                    end
                  when :key_normal then
                    case char
                    when '=' then state = :value
                    when 'a'..'z', 'A'..'Z', '0'..'9', '-', ' ' then key << char
                    else raise(MalformedError, "Unrecognized RDN attribute type name character \"#{char}\"")
                    end
                  when :key_oid then
                    case char
                    when '=' then state = :value
                    when '0'..'9', '.', ' ' then key << char
                    else raise(MalformedError, "Unrecognized RDN OID attribute type name character \"#{char}\"")
                    end
                  when :value then
                    case char
                    when '\\' then state = :value_normal_escape
                    when '"' then state = :value_quoted
                    when ' ' then state = :value
                    when '#' then
                      state = :value_hexstring
                      value << char
                    when ',' then
                      state = :key
                      yield key.string.strip, rstrip_except_escaped(value.string, dn_index)
                      key = StringIO.new
                      value = StringIO.new
                    else
                      state = :value_normal
                      value << char
                    end
                  when :value_normal then
                    case char
                    when '\\' then state = :value_normal_escape
                    when ',' then
                      state = :key
                      yield key.string.strip, rstrip_except_escaped(value.string, dn_index)
                      key = StringIO.new
                      value = StringIO.new
                    when '+' then raise(UnsupportedError, "Multivalued RDNs are not supported")
                    else value << char
                    end
                  when :value_normal_escape then
                    case char
                    when '0'..'9', 'a'..'f', 'A'..'F' then
                      state = :value_normal_escape_hex
                      hex_buffer = char
                    else
                      state = :value_normal
                      value << char
                    end
                  when :value_normal_escape_hex then
                    case char
                    when '0'..'9', 'a'..'f', 'A'..'F' then
                      state = :value_normal
                      value << "#{hex_buffer}#{char}".to_i(16).chr
                    else raise(MalformedError, "Invalid escaped hex code \"\\#{hex_buffer}#{char}\"")
                    end
                  when :value_quoted then
                    case char
                    when '\\' then state = :value_quoted_escape
                    when '"' then state = :value_end
                    else value << char
                    end
                  when :value_quoted_escape then
                    case char
                    when '0'..'9', 'a'..'f', 'A'..'F' then
                      state = :value_quoted_escape_hex
                      hex_buffer = char
                    else
                      state = :value_quoted
                      value << char
                    end
                  when :value_quoted_escape_hex then
                    case char
                    when '0'..'9', 'a'..'f', 'A'..'F' then
                      state = :value_quoted
                      value << "#{hex_buffer}#{char}".to_i(16).chr
                    else raise(MalformedError, "Expected the second character of a hex pair inside a double quoted value, but got \"#{char}\"")
                    end
                  when :value_hexstring then
                    case char
                    when '0'..'9', 'a'..'f', 'A'..'F' then
                      state = :value_hexstring_hex
                      value << char
                    when ' ' then state = :value_end
                    when ',' then
                      state = :key
                      yield key.string.strip, rstrip_except_escaped(value.string, dn_index)
                      key = StringIO.new
                      value = StringIO.new
                    else raise(MalformedError, "Expected the first character of a hex pair, but got \"#{char}\"")
                    end
                  when :value_hexstring_hex then
                    case char
                    when '0'..'9', 'a'..'f', 'A'..'F' then
                      state = :value_hexstring
                      value << char
                    else raise(MalformedError, "Expected the second character of a hex pair, but got \"#{char}\"")
                    end
                  when :value_end then
                    case char
                    when ' ' then state = :value_end
                    when ',' then
                      state = :key
                      yield key.string.strip, rstrip_except_escaped(value.string, dn_index)
                      key = StringIO.new
                      value = StringIO.new
                    else raise(MalformedError, "Expected the end of an attribute value, but got \"#{char}\"")
                    end
                  else raise "Fell out of state machine"
                  end
                end

                # Last pair
                raise(MalformedError, 'DN string ended unexpectedly') unless
                  [:value, :value_normal, :value_hexstring, :value_end].include? state

                yield key.string.strip, rstrip_except_escaped(value.string, @dn.length)
              end

              def rstrip_except_escaped(str, dn_index)
                str_ends_with_whitespace = str.match(/\s\z/)

                if str_ends_with_whitespace
                  dn_part_ends_with_escaped_whitespace = @dn[0, dn_index].match(/\\(\s+)\z/)

                  if dn_part_ends_with_escaped_whitespace
                    dn_part_rwhitespace = dn_part_ends_with_escaped_whitespace[1]
                    num_chars_to_remove = dn_part_rwhitespace.length - 1
                    str = str[0, str.length - num_chars_to_remove]
                  else
                    str.rstrip!
                  end
                end

                str
              end

              ##
              # Returns the DN as an array in the form expected by the constructor.
              def to_a
                a = []
                self.each_pair { |key, value| a << key << value } unless @dn.empty?
                a
              end

              ##
              # Return the DN as an escaped string.
              def to_s
                @dn
              end

              ##
              # Return the DN as an escaped and normalized string.
              def to_normalized_s
                self.class.new(*to_a).to_s.downcase
              end

              # https://tools.ietf.org/html/rfc4514 section 2.4 lists these exceptions
              # for DN values. All of the following must be escaped in any normal string
              # using a single backslash ('\') as escape. The space character is left
              # out here because in a "normalized" string, spaces should only be escaped
              # if necessary (i.e. leading or trailing space).
              NORMAL_ESCAPES = [',', '+', '"', '\\', '<', '>', ';', '='].freeze

              # The following must be represented as escaped hex
              HEX_ESCAPES = {
                "\n" => '\0a',
                "\r" => '\0d'
              }.freeze

              # Compiled character class regexp using the keys from the above hash, and
              # checking for a space or # at the start, or space at the end, of the
              # string.
              ESCAPE_RE = Regexp.new("(^ |^#| $|[" +
                                    NORMAL_ESCAPES.map { |e| Regexp.escape(e) }.join +
                                    "])")

              HEX_ESCAPE_RE = Regexp.new("([" +
                                    HEX_ESCAPES.keys.map { |e| Regexp.escape(e) }.join +
                                    "])")

              ##
              # Escape a string for use in a DN value
              def self.escape(string)
                escaped = string.gsub(ESCAPE_RE) { |char| "\\" + char }
                escaped.gsub(HEX_ESCAPE_RE) { |char| HEX_ESCAPES[char] }
              end

              private

              def initialize_array(args)
                buffer = StringIO.new

                args.each_with_index do |arg, index|
                  if index.even? # key
                    buffer << "," if index > 0
                    buffer << arg
                  else # value
                    buffer << "="
                    buffer << self.class.escape(arg)
                  end
                end

                @dn = buffer.string
              end

              def initialize_string(arg)
                @dn = arg.to_s
              end

              ##
              # Proxy all other requests to the string object, because a DN is mainly
              # used within the library as a string
              # rubocop:disable GitlabSecurity/PublicSend
              def method_missing(method, *args, &block)
                @dn.send(method, *args, &block)
              end

              ##
              # Redefined to be consistent with redefined `method_missing` behavior
              def respond_to?(sym, include_private = false)
                @dn.respond_to?(sym, include_private)
              end
            end
          end
        end
      end

      def perform(start_id, end_id)
        return unless migrate?

        ldap_identities = Identity.where("provider like 'ldap%'").where(id: start_id..end_id)
        ldap_identities.each do |identity|
          begin
            identity.extern_uid = Gitlab::Auth::LDAP::DN.new(identity.extern_uid).to_normalized_s
            unless identity.save
              Rails.logger.info "Unable to normalize \"#{identity.extern_uid}\". Skipping."
            end
          rescue Gitlab::Auth::LDAP::DN::FormatError => e
            Rails.logger.info "Unable to normalize \"#{identity.extern_uid}\" due to \"#{e.message}\". Skipping."
          end
        end
      end

      def migrate?
        Identity.table_exists?
      end
    end
  end
end
